Elsevier

Biochimie

Volume 119, December 2015, Pages 52-59
Biochimie

Research paper
6-O-Veratroyl catalpol suppresses pro-inflammatory cytokines via regulation of extracellular signal-regulated kinase and nuclear factor-κB in human monocytic cells

https://doi.org/10.1016/j.biochi.2015.10.006Get rights and content

Highlights

  • 6-O-Veratroyl catalpol inhibits IL-1β and TNF-α expression in THP-1 cells stimulated by PMA.

  • 6-O-Veratroyl catalpol suppresses PKC/ERK/NF-κB signaling in THP-1 cells stimulated by PMA.

  • 6-O-Veratroyl catalpol regulates TNF-α promoter activity via PKC.

Abstract

The compound 6-O-veratroyl catalpol (6-O) is a bioactive iridoid glucoside that was originally isolated from Pseudolysimachion rotundum var. subintegrum. It has been demonstrated that catapol derivative iridoid glucosides including 6-O, possess anti-inflammatory activity in carragenan-induced paw edema mouse model as well as bronchoalveolar lavage fluid of ovalbumin-induced mouse model. In the present study, we investigated whether 6-O modulates inflammatory responses in THP-1 monocytic cells stimulated with phorbol12-myristate-13-acetate (PMA). Our data showed that 6-O inhibited PMA induced interleukin (IL)-1β and tumor necrosis factor (TNF)-α expression in THP-1 monocytic cells. Mechanistic studies revealed that 6-O suppressed the activity of protein kinase C (PKC), which further resulted in downstream inactivation of extracellular signal-regulated kinase (ERK) and nuclear factor-κB (NF-κB) inflammatory pathway. The results implied that 6-O may protect against inflammatory responses that could be a potential compound in treating inflammatory diseases.

Introduction

Inflammation is a body normal defense induced by pathogens and toxic stimuli such as physical injury or chemicals [1], [2]. Acute inflammation is an immediate response that usually results in healing while chronic inflammation is a long-term medical condition that is involved in active inflammation. Such persistent inflammation may lead to severe diseases such as allergy, cancer, arthritis, and autoimmune diseases. Although inflammatory responses exert in different diseases, the most important group controlling these phenomenon likely be inflammatory cytokines and mediators [3]. Protein kinase C (PKC) family members, consisting of 12 phospholipid-dependent serine/threonine kinases, have been demonstrated involving in cell migration and proliferation [4], [5]. The tumor promoter phorbol-12-myristate-13-acetate (PMA) has been shown to induce the enzyme protein kinase C (PKC) as PMA can substitute for diacylglycerol (DAG) in promoting classical and non-conventional PKC isoforms [6]. It has been reported that PKCs are able to activate the mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB) pathways which finally leads to the release of pro-inflammatory cytokines or mediators [7], [8], [9], [10]. Therefore, PMA-induced inflammation is implicated in releasing of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, chemokine (C–C motif) ligand 5 (CCL5), and other mediators such as inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2 [11], [12], [13], [14]. Thus, in this study, applying PMA-stimulated human monocytic leukemia cell line THP-1, we investigated the signaling pathway activated by PKC and the anti-inflammatory effects of 6-O-veratroyl catalpol (6-O).

Pseudolysimachion genus plant, and the catalpol derivatives isolated therefrom, possesses anti-inflammatory, antiallergic and anti-asthmatic activity. According to that, we isolated 6-O from Pseudolysimachion genus plant to figure out its biological effect. 6-O (C24H30O13) with molecular formula as described in Fig. 1A has been previously mentioned as a bioactive compound for various inflammatory disorders. Studies have suggested that 6-O shows inhibitory effect on elevated IgE, IL-4 and IL-13 levels and eosinophilia in the plasma and bronchoalveolar lavage fluid (BALF), and mucus overproduction in the lung tissues in an ovalbumin (OVA)-induced asthmatic mouse model [15]. However, the underlying mechanism of 6-O on anti-inflammation is not well understood. In this study, we isolated 6-O from Pseudolysimachion rotundum var. subintegrum, and investigated its inhibitory mechanism on the inflammatory reaction in PMA-stimulated THP-1 cells.

Section snippets

Cell culture

We obtained the human THP-1 monocyte and A549 cell line from the American Type Culture Collection (ATCC, Rockville, MD, USA). The cells were cultured in Roswell Park Memorial Institute (RPMI) medium (Welgene Incorporation, Daegu, Korea) supplemented with 10% (v/v) heat-inactivated fetal bovine serum (FBS, Hyclone Laboratories, Logan, UT, USA). The cells were incubated under an atmosphere of 5% CO2 at 37 °C and were subjected to a maximum of 20 cell passages.

Reagents

The dried stems and leaves of

Results and discussion

Inflammation is a complex process initiated by organisms, to remove injurious stimuli. However, excessive inflammation can itself lead to severe diseases, such as asthma, rheumatoid arthritis, and even cancer [19]. Pseudolysimachion rotundum belonged to Pseudolysimachion genus, is a perennial herb distributed in Korea, China, Russia and Europe. The previous reports have been demonstrated that the extract of Pseudolysimachion rotundum and the catalpol derivatives isolated therefrom, show the

Acknowledgments

This research was supported from Konkuk University 2015.

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